Linear and cyclic organo(poly)siloxanes containing Si-linked butadienyl and 3-methylbutadienyl groups are described in German Auslegeschrift 1,210,846 and GB-A 1,081,150. They are prepared by adding vinylacetylene and isopropenylacetylene, respectively, to an organo(poly)siloxane having at least one Si-linked hydrogen atom in the presence of a catalyst which promotes the addition of Si-linked hydrogen to an aliphatic multiple bond. Vinylacetylene is gaseous, so that the reaction must be carried out under pressure, and it has a tendency to explode. The yields in the process are only moderate.
The addition of 3-methyl-l-butyn-3-ol to organosilicon compounds containing Si-linked hydrogen in the presence of hexachloroplatinic acid is described in U.S. Pat. No. 2,823,218 to Speier et al. It is also known from Chemical Abstracts 51, 9474f, 1957 that 2-triethylsilyl-3-methyl-1,3-butadiene can be obtained by elimination of water when 2-triethylsilyl-3-methyl-1-buten-3-ol is heated in the presence of KHSO.sub.4.
It was expected from Chemical Abstracts 51, 9474f, 1957, that butadienyl-functional organo(poly)siloxanes would crosslink in the presence of acids which promote the cationic polymerization of the butadienyl groups.
Surprisingly, applicants have found that butadienyl-functional organo(poly)siloxanes can be prepared without crosslinking in the presence of acids.
It is, therefore, an object of the present invention to prepare organo(poly)siloxanes having Si-linked conjugated dienyl groups in a simple process, from readily available compounds and in good yields. A further object of the present invention is to prepare organo(poly)siloxanes having Si-linked, conjugated dienyl compounds without using pressure.